I would use enough of the IAL to stain the water to a nice amber color, tear them up in pieces if you don't already and if you have carbon in the filter remove it and IMO I would turn the filter off the current can cause fin damage and IMO/E more water changes are better anyway especially for the CT delicate fins.

You can pre-mix your water and keep IAL in the pre-mix, you can even make a tea out of the IAL just pour hot not boiling water over them and let them steep 5 min or so, dump that water and repeat to get all the tannins out of the leaf and keep in a clean jug, dilute and use for water changes.

I use native oak leave, they do the same as the IAL, I have used the IAL in the past and I used 1 large to 5g of water and left them in the tank until they fell apart, I do the same with the oak leave, I like the nylon idea that would make for easy cleanup...lol....

Here is an awesome sponge you can put over your intake. I've had one on mine for months with absolutely no problem (but I do take it off and rinse it during water changes). You can get it at petsmart for about $2.50. I use them on all my filters with intake tubes.

One thing I would try is to stop using the salt. Salt hardens the water while IAL softens the water. Since bettas prefer the softer water I would use only the IAL to see how it works, just keep an eye on your pH to make sure it doesn't change drastically.